Automatic telephone system



T. G. MARTIN AUTOMATIC TELEPHONE SYSTEM April 13 1926.

Original Filed March 5, 1922 Patented Apr. 13, 1926.

UNITED STATES PATENT OFFICE.

TALBOT G. MARTIN, on CHICAGO, ILLINOIS, ASSIGNOR, BY 'MESNE ASSIGNMENTS, T0 AUTOMATIC ELECTRIC INC., on CHICAGO, ILLINOIS, A CORPORATION OF DELA- 'W'ARE.

Application filedMarch 3, 15122,

To all whom it may concern:

Be it known that I, TALBOT G. MARTIN, a citizen of the United States of America, and

a resident of Chicago, Cook County, and

ploy both primary and secondary line switches for the purpose of connecting calling lines with idle'first selector switches; and the object of the invention is the provision of certain improvements in a system of this kind which tend to increase its commercial utility. contemplates the use of secondary line switches of the rotary type, and improved arrangements are shown whereby such switches may be used to advantage in conjunction with primary well known Keith or plunger type.

In systems of this general character, it has been customary to provide an arrangementof chain relays for a group of secondary line switc-heswhich will operate to make all the secondary line switches busy to the primary line switches whenever all ofthe trunk lines accessible to the group of secondary line switches become busy. This busyi-ng means, however, does not become effective until the last trunk line has actually been taken for use by a secondary line switch, and it may happen therefore that two or more secondary line switches are seized and'started hunting for trunk lines at a time when there is only one trunk line available. In such a case the first line switch to reach the idle trunk line will take it for use, while the other switch or switches will continue to hunt for trunks. Unless another trunk line becomes idle almost at once, the delay introduced is almost certain to spoil the calls, and the prolonged trunk hunting is consequently of no utility.

In order to suitably care for the above described situation, means is provided for rendering all the secondary line switches of a group inoperative whenever all of the trunks accessible to such group become busy. In ad dition, since it is desirable to know how often calls are lost because they are not diverted to other groups in time, a-meter is pro- In particular the invention line switches of the Serial N'o. 540,890. Renewed July 25, 192.3.

vided whichis operated to register the number of times the condition occurs.

The foregoing features will be described hereinafter with reference to the accompanying drawings, which show sufficient of the apparatus in an automatic telephone system to enable the invention to be explained and understood.

Referring to the drawing, the reference character A indicates an automatic telephone substation of the ordinary type having the usual talking instrumentalities and a calling device S for controlling the automatic switches at the exchange.

The line conductors 11 and 12 terminate at the exchange in the individual line switch C, which is a switch of the well known Keith or plunger type, and therefore will not need to be described in detail. Briefiv stated, the function of the line switch C is to extend the associated line when calling to an idle trunk line.

In accordance with the usual practice, the

lines entering the exchange are divided into' groups, andall of the line switches associated with the lines in each group may be controlled in theirtrunk selecting operations by a common master switch. The master switch which is associated with the group whichincludes the line switch C is shown in the lower left hand corner of the drawing and is indicated by the reference character MS. The function of the-master switch MS, as is well known, is to maintain the plungers of all idle line switches opposite an idle trunk line. i

Secondary line switches are employed in the present sy. em a.' d accordingly the trunk lines from the prnna-rv line switchboards will extend to secondary line switches. rather than to first selector switches. The arrangen'ient of the trunking between the primary and secondary line switchboards is well understrorl. There may be a plurality of groups .ofsecondary line switches and each group of primary line switches will have outgoing trunks extending to the secondary line switches in each secondary group, so that any subscriber calling will be given access to the trunk lines outgoing from all the secondary groups. In this manner a large number of first selectors, say one hundred or more, may be combined'in' one large group to secure an'--incre ased trunking eliiciency.

The advantages gained by the use of secondary line switches, however, are well known and need not be discussed in detail.

One of the trunk lines outgoing from the primary group which includes the line switch C is shown in the drawing and ex tends to the secondary line switch D. The line switch D is of the well known rotary type in which the wipers have no normal positions and move in a forward direction only.

The reference character indicates a selector switch of the well known Strowgcr vertical and rotary type of which only a portion of the circuits are shown.

To the right of the master switch MS is shown a-relay group which has certain functions to perform when all of the trunk lines outgoing from the secondary line switch group which includes the line switch D become busy. It will be more convenient, however, to describe their functions and operation later on during the explana tion of the operation of the system.

Having briefly described the apparatus involved, its operation will now be described more in detail with a view to pointing out the particular features of novelty disclosed herein. For this purpo;e it will be assumed that the subscriber at substation A desires to call some other subscriber in the system, and the operation of the primary and secondary line switches C and D in connecting the line of substation A to a trunk line eX- tending to a first selector switch will be described. When the receiver at substation A is removed a circuit is completed over the line conductors 11 and 12 for the line relay 1% of the line switch C. Upon energizing, the line relay l4: closes a circuit for the pull in winding 15 of the line switch C at armature Upon energizing, the pull in winding operates both the cut-ell arn1a ture 21 and the plunger arm 22, the former being effective to disconnect the line conductors 12 and 11 from the winding of the line relay and from ground, respectively; while the latter forces the bank springs 30, 31, and into engagement with contacts 34, 36, and 87, respectively. By the engagement of bank springs 30 and 33 with contacts 3% and 37, the line conductors 11 2 are extended into connection with the runk line conductors and i2, and a cirruit is accordingly completed for the line relay of the secondary line switch D. The line relay 5 is energized and at its armature 53 a holding circuit for line switch C completed, which may be traced from ground by the way of the working contact of armature 53 and said armature, normally closed contact springs controlled by armature release trunk conductor l-l, contact 35, bank spring 31, and the holding winding 16 of the line switch C to battery. This iolding circuit is established before the slow acting line relay l l of the line switch C- has had time to deenergize and is effective to retain the plunger arm 22 and the cutoff armature 2i in an operated position. A ground potential is also placed on the private normal conductor 18 which is connected with the multiple test contacts in the banks of the connectors which have access to the line of substation A, whereby the line is guarded against intrusion in the customary manner.

A circuit for the master switch MS is closed by the engagement of bank spring 32 with contact 36. The master switch is thus operated in the usual manner to advance the plungcrs of all t..ie die line switches in the group into position .11 front of the next idle trunk.

lVhen the line relay 50 of the secondar; line switch is energized, as explained before, a circuit is closed at its armature including the winding of the switching relay 51 and the winding of the stepping magnet in series, while at the same time by means of armature the test wiper 66 is connected to this circuit at a point midway between the said relay and said magnet. The operation now depends upon whether the trunk line with which the wipers are in engagement is busy or idle. If the trunk line is busy there will be a ground potential on the test contact engaged by the test wiper 66, the switching relay will be short circuited, and the stepping magnet, which interrupts its" own circuit, will operate in the same manner a buzzer to advance the switch wipers step by step until an idle trunk line is found. F/ hen the wipers arrive at an idle trunl: line, which we may assume is the trunk line comprising con doctors 71, 72, and 73, the test wiper 66 will find no ground potential on the test contact 69, the rotation of the switch will cease, and the switching relay 51, being no longer short circuitcd, will energize in series with the stepping magnet the latter magnet remaining inoperative on account of the high resis ice of switching relay. Upon energizing, relay connects the incoming release or ll to the test wiper 6G by meal at armature 57 and its working contact locks itself to the grounded release conductor. Ground at the working contact of armature maintained on the test wiper 66 until a. holding circuit 1" om idle selector E has been established, this ground also rendering the selected trunk line busy. In addition to the foregol at armatures 56 and 59 relay 5i disc; 5: the incoming trunk conductors and 42 from the windings of the relay 50 and from ground, rc spcctivcly, and ettcncs them by the way of wipers and 6?, bank contacts and 70,

conductors T1 and T3, and armatures Ti and meow-e0 E are well known its operation is well understood and it will be suflicient to state that i the line relay is energized over the circuit of the calling line and a circuit is closed for the associated slow acting release relay S1. The latter relay, upon energizing, places a ground potential upon the release conductor 72 at armature 84 and its working contact, thereby establishing a holding circuit for the switching relay 51 of the line switch D, and the holding winding 16 otthe primary line switch C. This holding circuit, it will be understood, is established before the slow acting line relay 50 has had time to deen-ergize.

The act of groundingrelease conductor 72, in addition to establishing the above mentioned holding circuit, completes an encrgizing circuit for the chain relay 87, and said relay maintains its armature in an operated position as long as the trunk-line is busy. The chain relays, of which only a portion are shown, are energized in this manner when the trunk lines with which they are associated become busy. Each chain relay upon energizingcloses its portion of a chain of 'contactsthrough which the'circuit for relay 88 is finally completed when all the chain relays are energized. Y

The remainder of the operations in which the calling subscriber controls the first selector taken for use, other automatic switches throughthe medium of his calling device S to complete the connection to the desired called line, are

well understood and as they have nothing special to do with the present invention, these operations will not be further (1011-, sidered, except to subscriber has finished talking, the restoration of his receiver to the switch-hook causes the automatic switches to restore to normal with the result that ground is disconnected from the release trunk conductor 72. This operation breaks the holding circuit for primary and secondary line switches C and D and said switches are restored to normal position.

Having described the system in a general way, it will be convenient now to explain the novel features which have been incorporated therein.

In order to explain these features we will assume that two subscribers have seized secondary line switches, one of which is the line switch D and the other of which a line switchin the same secondary group, at a time when the trunk line shown is the only remaining idle selector trunk. Both secondary line switches start hunting for the idle trunk line and it will be assumed that the other line switch, which for convenience or line switch D and a plurality of say that when the calling we will call D, seizes the last remaining idle trunk line before the line switch D has time to seize it. When the other line switch. seizes the trunk line its chain relay 87 is energized in the same manner as previously described and cornpletes the energizing circuit for relay 88. The relay 88 removes at its armature 92 and its resting contact the short circuit around the lost call relay '90, and at this time an energizing circuit may be traced for relay as follows: vFrom ground'by the way of relay 90, conductor 97, resting contact of armature 59 and said armature, conductor 2, over the subscribers loop as previously traced to conductor 40, armature 56 and'its resting contact, and winding of relay 50 1;0 battery. The line relay 50 is adapted to deenergize in series with relay 90 on account of the high resistance of the winding of relay 90. The relay 90, however, is energized circuit is closed for thelost call meter M. The lost call meter is therefore operated to register the call.

VVhen the l'ne relay '50 of line switch D is deenergized, the circuit for the stepping magnet 52 isopened at armature 55. vbusy tone is also transmitted to the calling subscriber at armature 92 and its working vcontact in the usual manner, by which the subscriber isinformed thatthe desired connection cannot becompleted. I

The relay 88 at its armature '91 and its working contact completes an energizing circuit for the group 'busying relay 89. Relay 89, 'upon energizing, connects ground to the conductor 98 which is normally con- The ground thus 'placedon the release trunk conductor. usual manner. The group busyi-ng relay 89 has a conductor, such as conductor 98, for each secondary line-switch in the group and busys all these trunk lines at the same time'and in the same manner that the trunk 'line leading to line switch D is busied,

providing of course that the. trunk lines in question are not already busy. It the plunger shaft at any primary line switchboard is standing opposite any one of the busied trunk lines leading to this'group of secondaries, the master switch MS moves said shaft to bring the plungers into alignment/with a. trunkline leading to a different secondary group. g

It will be noted that the same ground from armature '94 that busys the trunk line extending to line switch D also maintains the plunger of the calling primary line switch C in anopera ted position so as to prevent the plunging in and out, or fluttering of the said primary line switch, when the relay 50 upon deenergizing removes the original holding ground.

nected with the release trunk conductor 4-1;

41 busys the trunk line in the.

and at its armature 93 a I After receiving the busy tone the subscriber hangs up and calls again later on. Upon the restoration of the receiver to the switchhool; the automatic switches are released in the same manner as previously explained.

As soon as one of the outgoing trunk lines from this secondary group becon'ie idle the chain relay individual thereto'deenergizcs and opens the circuit of relay 88, which relay upon deenergizing restores the relays 89 and 90 to their normal positions. llv the deenergization of relay 90 the circuit for the lost call meter is opened, allowing said meter to restore to normal, while the deenergization of relay S9 removes the busy condition from the secondary line switch.

Having described the invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

.Vhat I claim is:

1. In a telephone system, subscribers lines, a group of trunk lines, a group of secondary line switches having access to said trunk lines, primary line switches having access to said secondary line switches, means whereby a calling subscribe-r can operate his primary line switch and one oi said secondary line switches to connect with an idle one of said trunk lines, means for busying all the trunk lines of said group, a meter, and means rendered effective to operate said meter each time said trunk lines are made busy while the secondary line switch in use is still hunting for an idle trunk.

2. In a telephone system, subscribers lines, a,gronp of trunk lines, a group of rotary secondary line switches having access to said trunk lines, ')rimary line switches having access to said group of secondary line switches, means whereby a calling subscriber can operate his primary line switch and one of said secondary line switches to connect with an idle one of said trunk lines, and means for rendering said secondary line switch inoperative in case all of said trunk lines become busy before the said secondary line switch has completed the con nection.

3. In a telephone system, subscribers lines, a group of trunk lines. a group of secondary line switches having acce s to said trunk lines, primary line switches havaccess to said secondary line switches, means whereby a calling subscriber can operate his primary line switch and one ol said secondary line switches to connect with an idle one of said trunk lines, means for rendering said secondary line switch in operative in case all of said trunk lines become busy before the said secondary line switch has completed the connection, and means effective when said secondary line switch is made inoperative for maintaining the primary line switch in use in operated position until said calling subscriber hangs up.

4. In a telephone system, subscribers lines, trunk lines, groups of prinary line switches and a group of rotary secondary line switches for extending calling subwcribers lines to idle trunk lines, and means responsive to a busy condition of said trunk lines for rendering inoperative one of said secondary line switches after it has been seized for extending a call.

5. In a telephone system, subscribers lines, a group of trunk lines, a group of secondary line switches ha ing access to said trunk lines, primary line switches having access to said secondary line switches, means whereby calling subscribers can operate theirprimary line switches and a plurality of said secondary line switches to connect with idle trunk lines, means for busying all the trunk lines in said group, and means for counting the number of calls that are lost due to said trunk lines being made busy before all said secondary line switches have located idle trunks.

6. In a telephone system, subscribers lines, trunk lines, groups of primary line switches and a group of rotary secondary line switches for extending calling subscribers lines to idle trunk lines, and means responsive to a busy condition of said trunk lines for stopping one of said secondary line switches after it has been started operating to find an idle one or said trunk lines.

7. In a telephone system, subscribers lines, a group of trunk lines, a group of secondary line switches having access to said trunk lines, primary line switches having access to said secondary line switches, means whereby calling subscribers can operate their primary line switches and a plurality of said secondary line switches to connect with idle trunk lines, means for busying all the trunk lines in said group, and means for counting the number of calls that have been extended into connection with a secondary switch and are then lost due to said trunk lines being made busy while such secondary line switches are hunting for idle trunk lines.

In witness whereof, I hereunto subscribe my name this 27th day of February, A. 13., 1mg? TALBOT G. MARTIN.

Urad. 

